Many different arrangements are known for manufacturing a transfer case capable of transferring torque from the input shaft thereof to both a front and rear output shaft to provide four-wheel drive. One particular design utilizes a drive sprocket rotatably mounted about the drive shaft and connected by a chain to a second sprocket coupled to rotate with the front output shaft. During two wheel drive mode, the drive shaft rotates without transferring torque to the drive sprockets. However, when in four-wheel drive mode, the drive sprocket mounted about the drive shaft is coupled to the drive shaft to receive torque therefrom and transfer the torque through the drive chain to the front output shaft.
One method of selectively coupling the drive shaft to the drive sprocket is to provide a four-wheel drive clutch. The four-wheel drive clutch must be relatively large to be capable of transferring sufficient torque to drive the front wheels of the vehicle. However, the increasing popularity of four-wheel drive vehicles has led to the demand for smaller, lighter-weight, and less expensive transfer cases that may be used on trucks as well as passenger cars. The presence of a four-wheel drive clutch limits the ability of designers to reduce the size and weight of transfer cases.
Transfer cases may also be designed to provide a choice among a high speed range, a low speed range, or a neutral range. Although range shift operations are ordinarily performed when the motor vehicle transmission is in neutral, if the vehicle has an automatic transmission, the transmission may continue to transmit torque to the input shaft of the transfer case for a brief time because of a phenomenon known as torque converter drag. During range shift operations, such as when the vehicle driver shifts the transfer case from low or neutral into the high speed range or into the low speed range from the high speed range, the stationary components associated with the intermediate drive shaft of the transfer case must be coupled with the rotating torque input shaft or components connected thereto. Without a synchronizer/brake assembly, the torque converter drag causes a difference in rotational speed between the input shaft and the non-rotating intermediate drive shaft during coupling operations and evidences itself as ratcheting between the gears or clunking which results in noise, vibration, and wear on the shafts and gears.